1. Field of the Invention
The present invention relates to a hermetic type outdoor equipment provided with a respiratory structure capable of preventing invasion of rain water, dust, etc. into the equipment via a respiratory hole formed through a hermetic case to ensure entrance and exit of air. The present invention is applicable to a hermetic type equipment provided with the respiratory structure such as radio relay equipment which is disposed outdoors.
2. Description of the Related Art
In such a hermetic type outdoor equipment, the air in a case of the equipment is warmed by a thermal effect of solar radiation, and the inner pressure may be increased due to the difference between the temperature of the inner air and the temperature of the outside air. In order to avoid the increase of pressure in the case and to radiate the inner heat to the outside, a structure for respiration (respiratory structure) for exit of the air in the case to the outside and for entrance of the outside air into the case is required. Accordingly, it is a general method that a respiratory hole is formed at a bottom portion of the case or the like at which invasion of rain water can be avoided, and a mesh member or a minute-hole sheet is mounted on the respiratory hole to keep a desired respiratory action.
For example, as shown in FIG. 1, a respiratory hole 14 is formed in the bottom protion of a case 13 in which a device, not shown, is accommodated. A minute-hole sheet 15 made of synthetic resin is arranged in the case 13 at a position correspnding to the respiratory hole 14. A plate 16 having an opening 16a at a position corresponding to the respiratory hole 14 is superimposed to the minute-hole sheet 15. The plate 16 and minute-hole sheet 15 are fixed to the case 13 by means of screws 17.
As shown in FIG. 2, minute-holes 15a are formed in the entire region of the minute-hole sheet 15, and a central area 15b of the minute-hole sheet 15 is exposed to the outside via the respiratory hole 14.
Bird lice, etc. inhabiting the environment around the hermetic type outdoor equipment provided with the respiratory structure have such a behavior (thermal attraction) that they gather in the neighborhood of the respiratory hole 14 in response to specific temperature range atmosphere, particularly in a temperature range atmosphere which is generated by the exit of the heated inner air to the outside via the respiratory hole 14 due to their growth instinct, and thus the minute-hole sheet 15 is bit ten and broken by the bird lice gathering at the respiratory hole 14, so that the bird lice are allowed to invade into the case 13 and thus cause the failure of the device.